A typical vehicle or platform (such as an aircraft, UAV, boat, car, or truck) is capable of moving in one or more directions. Such a platform may include absolute attitude determination capability which allows the platform to utilize various sensors to ascertain the current platform attitude relative to a fixed external reference. The attitude of a platform is its orientation with respect to this defined frame of reference.
An Inertial Navigation System (INS) is a navigation aid that uses a computer and motion sensors to continuously track the position, orientation, and velocity (direction and speed of movement) of a vehicle without the need for external references. An inertial navigation system includes at least a computer and a module containing accelerometers, gyroscopes, or other motion-sensing devices. The INS is initially provided with its position and velocity from another source (a human operator, a GPS satellite receiver, etc.), and thereafter computes its own updated position and velocity by integrating information received from the motion sensors. A feature of an INS is that it requires no external references in order to determine its position, orientation, or velocity once it has been initialized. Some INSs place the accelerometers on a vibrationally isolated module such as a gimbaled gyrostabilized module.